Known tracking techniques often utilize the angle of arrival (or arrival angle) of an incoming signal to determine a position of one platform relative to another platform. The platforms may be stationary or moving relative to each other. In some applications, one platform is stationary and the other platform is moving. In yet other applications, both platforms are moving. In a common application, the platform transmitting the signal is stationary and the platform receiving the signal is moving. For example, in aerospace applications, the signal-transmitting platform can be a flight control element positioned on the ground and the signal-receiving platform can be an aircraft in flight (e.g., airborne). In such applications, the angle of arrival is defined as the angle between the direction of the signal received by the aircraft (which corresponds with the position of the signal-transmitting platform) and the orientation of the aircraft. The orientation of the aircraft is commonly associated with the direction of travel of the aircraft.
Certain conventional tracking techniques determine the angle of arrival of a signal from a signal-transmitting platform by comparing the characteristics of signals received by two or more spaced-apart, signal-receiving aircraft. The signal characteristics may include the time of arrival of the signal at the two signal-receiving aircraft and/or the frequency of arrival of the signal at the two signal-receiving aircraft. The geographical diversity between the two signal-receiving aircraft and the relative velocities of the aircraft promoted the accuracy of such multi-platform techniques. However, such multi-platform techniques require two or more aircraft for proper execution, which may be difficult and costly to implement. Accordingly, in many instances, determining the angle of arrival of a signal at a signal-receiving aircraft independent of other signal-receiving aircraft or platforms is desirable.
Some single-platform tracking techniques determine the angle of arrival of an incoming signal at a signal-receiving aircraft, without relying on other signal-receiving aircraft or platforms. Such single-platform techniques are based on a difference in the time of arrival of the signal at two different antennas on the aircraft and/or a difference in the frequency of arrival of the signal at the two different antennas. However, because the distance between the antennas on the aircraft is negligible and the antennas are not moving relative to each other, the use of time-difference-of-arrival (TDOA) techniques and frequency-difference-on-arrival (FDOA) techniques often resulted in inaccurate estimations of the angle of arrival.